Configuring Multicast Distributed Switching

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Configuring Multicast Distributed Switching" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Advantages of Multicast Distributed Switching

Switching multicast traffic at the RP had the following disadvantages:

•The load on the RP increased. This affected important route updates and calculations (for Border Gateway Protocol (BGP), among others) and could stall the router if the multicast load was substantial.

•The net multicast performance was limited to what a single RP could switch.

MDS solves these problems by performing distributed switching of multicast packets received at the line cards (Versatile Interface Processors [VIPs] in the case of RSP, and line cards in the case of Cisco 12000 series router). The line card is the interface card that houses the VIPs (in the case of RSP) and the line card (in the case of Cisco 12000 series router). MDS is accomplished using a forwarding data structure called a Multicast Forwarding Information Base (MFIB), which is a subset of the routing table. A copy of MFIB runs on each line card and is always kept up to date with the MFIB table of the RP.

MDS can work in conjunction with Cisco Express Forwarding or unicast distributed fast switching (DFS).

Starting with Cisco IOS Release 11.2GS, IP multicast traffic can be distributed switched on RSP-based platforms with VIPs. MDS is the only multicast switching method on the Cisco 12000 series router starting with Cisco IOS Release 11.2(11)GS.

Multicast Distributed Switching Is Disabled by Default

On the Cisco 7500 series router, the default is IP multicast fast switching. MDS is an option that is available and is disabled by default.

On the Cisco 12000 series routers, MDS is also disabled by default. To switch multicast packets on the Cisco 12000 series router, you need to configure all interfaces for MDS. MDS is the only multicast switching mode for the Cisco 12000 series router.

If MDS is not enabled on an incoming interface that is capable of MDS, incoming multicast packets are not distributed switched; the multicast packets are fast switched at the RP. Also, if the incoming interface is not capable of MDS, packets are fast switched or process-switched at the RP.

If MDS is enabled on the incoming interface, but at least one of the outgoing interfaces cannot fast switch, packets are process switched.

Note We recommended that you disable fast switching on any interface when MDS is enabled.

Configuring Multicast Distributed Switching

Perform the following task to configure MDS. To configure MDS, you must enable it globally and on at least one interface because MDS is an attribute of the interface.

SUMMARY STEPS

1. enable

2. configureterminal

3. ip multicast-routingdistributed

4. interfacetypenumber

5. ip route-cachedistributed

6. ip mroute-cachedistributed

7. Repeat Steps 4 through 6 for each interface that you want to perform MDS.

8. end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

ip multicast-routingdistributed

Example:

Router(config)# ip multicast-routing distributed

Enables IP multicast routing.

•The distributed keyword enables MDS globally.

Step 4

interfacetypenumber

Example:

Router(config)# interface ethernet 0

Configures an interface type and enters interface configuration mode.

•The type argument is the type of interface to be configured.

•The number argument is the port, connector, or interface card number. The numbers are assigned at the factory at the time of installation or when added to a system, and can be displayed with the show interfaces command.

Step 5

ip route-cachedistributed

Example:

Router(config-if)# ip route-cache distributed

Enables distributed switching on the RSP.

Note This step is required on the RSP platform only.

Step 6

ip mroute-cache distributed

Example:

Router(config-if)# ip mroute-cache distributed

Enables MDS on the interface.

For Cisco 7500 series routers, this keyword is optional; if it is omitted, fast switching occurs. For Cisco 12000 series, this keyword is required because the Cisco 12000 series does only distributed switching.

Step 7

Repeat Steps 4 through 6 for each interface that you want to perform MDS.

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Step 8

end

Example:

Router(config-if)# end

Exits to privileged EXEC mode.

Note When you enable an interface to perform distributed switching of incoming multicast packets, you are configuring the physical interface, not the logical interface (subinterface). All subinterfaces are included in the physical interface.

–Name of the multicast group, as defined in the Domain Name System (DNS) hosts table or with the ip host command.

–IP address of the multicast group. This is a multicast IP address in four-part dotted-decimal notation.

•The source argument is a name or address of a multicast source that is sending to the group. A source need not be a member of the group. If you specify a group name or address, you can also specify a source name or address.

RFCs

RFC

Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

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Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

Feature Information for Configuring Multicast Distributed Switching

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

This table is intentionally left blank because no features were introduced or modified in Cisco IOS Release 12.2(1) or later. This table will be updated when feature information is added to this module.

line card—A general term for an interface processor that can be used in various Cisco products. For example, a Versatile Interface Processor (VIP) is a line card for the Cisco 7500 series router.

MFIB—Multicast Forwarding Information Base. A protocol-independent multicast forwarding system that contains unique multicast forwarding entries for each source or group pair known in a given network. There is a separate MFIB for every logical network (VPN) in which the router is configured. Each MFIB entry resolves a given source or group pair to an incoming interface (IIF) for reverse forwarding (RPF) checking and an outgoing interface list (olist) for multicast forwarding.

RP—Route Processor. The processor module in the Cisco 7000 series routers that contains the CPU, system software, and most of the memory components that are used in the router. It is sometimes called a supervisory processor.

RSP—Route Switch Processor. Processor module in the Cisco 7000 series routers that integrates the functions of the Route Processor (RP) and the Switch processor (SP).

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.